Method of making refractory products and the like



June 11, 1935.

C. M MULLEN METHOD OF MAKING REFRACTORY PRODUCTS AND THE LIKE Filed Dec. 18, 1933 INVENTOR. CHARLES MFMULLEN ATTORNEY.

Patented June 11, 1935 METHOD OF MAKING REFRACTORY PROD- UCTS AND THE LIKE Charles McMullen, Niagara Falls, N. Y., assignor to The Carborundum Company, Niagara Falls, N. Y., a corporation of Pennsylvania Application December 18, 1933, Serial No. 702,940

7 Claims.

This invention relates to a method of making special'shapes such as crucibles, hollow cores, hollow spheres, nozzles, etc.'from molten nonmetallic fusions such as molten refractory oxides. This invention has particular utility in the forming of special refractory shapes, that previously could not be made, of which an example are hollow spheres of fused alumina. Another advantage is that cracking by shrinkage in those cases where solid cores would ordinarily be used, is avoided.

I have discovered that if the cores used to form the openings in these special shapes are made of particular metals, having melting points below the non-metallic materials, the molten oxides or other molten refractory material when poured into the mold forms a solid layer about this core, the metal in turn being melted as the pouring continues. In order that the material surrounding and immediately adjacent to the core may become solid before the core becomes fluid and incapable of imparting its shape to the casting, and in order that the core may at the proper time become molten, it is obvious that particularly in castings having large cavities the dimensions and weight of the core must bear a suitable relation to the mass of the casting. This relation is readily calculable or may be determined by trial and error methods. After the casting operation the molten metal may be drained from the mold. I have found certain metals to be particularly suited to my purpose. The metal should have low viscosity when melted, so as to flow away from the casting readily as it melts. The metal should furthermore have a definite melting point. To facilitate casting, so as to obtain a sharp clean face, the metal should have good thermal conductivity so as to rapidly carry away the heat of the cast material in contact with the core, and form a skin of solidified material about the core. Examples of metals which are suitable for my purpose, depending upon the material to be cast, are copper, lead, aluminum and certain fusible grades of cast iron.

The drawing illustrates various ways in which my invention may be carried out. In the drawing, which is intended merely as explanatory of certain examples of apparatus which may be used in practising my invention, and not as limiting the invention, each of the figures is a vertical section through the molding apparatus. In Figures 1 and 3 the core is shown in elevation while in Figure 2 the spherical core is shown in section.

As one example of my method, a solid cast crucible of fused alumina can be made by pouring the molten alumina which has been fused in an electric furnace into a mold such as the one diagrammatically shown in vertical section in Figure 1. The mold 4 of suitable refractory material is securely mounted on a base 5 of similar material. A receptacle 6 is disposed beneath the base 5, and communicates with the mold cavity by way of a perforation or other opening 8. A core 9, in the example illustrated a cylinder, is mounted over the opening 8; and for greater security against being displaced by the flow of molten alumina into the mold, the core may have a small projection entered in the opening 8 to position the core. Openings II are provided at the top of the mold to serve as the inlet and vent, respectively.

In the case of alumina and a number of other refractory oxides, I have found copper to be a particularly desirable core material. While the copper core chills the molten alumina as soon as the two come in contact; the copper core, probably on account of its high thermal conductivity, remains intact until it is entirely enclosed by the alumina. The metal then melts and flows out of the bottom of the mold through the perforation 8, allowing the cast alumina shape to cool without cracking, as it would if the core were a solid one. The floor of the receptacle 6 into which the melted metal flows is preferably covered with some form of granular carbon l3 so that the metal does not oxidize. In this way the metal loss is kept at a minimum and discoloration and other defects in' the cast ware on account of metallic oxide vapors are avoided.

Figure 2 is a vertical section of a mold and metal core for making hollow spheres.- In this form of casting apparatus, the mold halves I5 and I6 are split along an equatorial plane of a the spherical mold cavity provided in the mold. Openings H, which communicate with the uppermost part of the mold cavity, serve as the inlet and vent respectively. The spherical core I8 is formed with a stem l9 which is gripped in the opening 20 leading from the mold cavity downwardly into the receptacle 2|. Granular carbon 22, as before, is spread on the floor of the receptacle 2|.

Figure 3 shows a mold for making a refractory piece with a slag tap hole. The outer case or mold proper may be made of refractory grains bonded with a temporary bond such as glutrin. The mold may be made either monolithic or sectional according to regular molding methods adapted to the making of cast refractory articles.- In some cases the outer mold may be of metal more refractory than the core metal. As shown, the

sections 24 and 25 of the mold are provided with recesses 26 and 21 for positioning a cylindrical metallic core 28 across the mold cavity from top to bottom. From the lower recess 21 an outlet 30 leads into a receptacle 3| containing granular carbon'32. The mold section 24 is furnished with an inlet 34 and vents 35.

The metallic core may, as these examples indicate, be made in various ways depending largely on the shape and size of the core. In the case of cylindrical and similar cores, e. g., the core in Figure 3, commercial bars may be used after being machined or otherwise shaped. More complicated shapes may be made by casting, this last method being particularly useful when a large number of similar cores are being made. Cores can also be made by bonding metallic powder or grain with binding materials such as pitch, e. g., in

,making the cores for the mold of Figure 2 for making hollow spheres.

In the casting of fused alumina the fusion may be made in an electric furnace of the pot type, in

which the carbon electrode depend. From the furnace, the molten material is poured into the mold by either tapping or tilting the furnace. After casting, the formed article is slowly cooled, either by insulating the entire mold containingthe cast article; or if the article is removed from the mold, it is slowly cooled in a furnace or by being buried within insulating material.

While I have described the application of this new casting method to the making of cast refractories, as that is a field in which it has its chief commercial use, it can also be used in making numerous other non-metallic and ceramic articles, e. g., hollow alumina grinding balls (these hard, tough grinding balls being afterwards filled with a heavy metal like lead in order to increase grinding efficiency), mortars, brake blocks, etc.

I have described specifically the use of alumina as a cast ingredient, but the method is also useful in the casting of other refractory materials, e. g., mullite, magnesia, spinel, chromite, various silicates, fluorides, including glasses. I have described the use of copper as the core metal, but other metals may be used particularly when the cast material is of a lower melting point.

I claim:

1. In the method of forming articles of nonmetallic refractory material, the steps which comprise casting said material in molten form into a mold and against a core of metal of high thermal conductivity having a melting point below that of the cast article, transferring heat from the casting to the core whereby theface of the casting in contact with the core becomes solidified and the core in turn thereafter becomes,

molten, and flowing the core from within the cast article.

2. In the method of forming articles of nonmetallic refractory material having a higher melting point than copper, the steps which comprise casting said material in molten form into a mold and against a core of copper, and transferring heat from the casting to the core whereby the face of the casting in contact with the core becomes rigid and the core thereafter becomes molten.

3. In the process of forming cast articles .of fused refractory oxideshaving a higher melting point than copper, the steps which comprise casting the molten oxides into a mold having a copper core and an outlet for said core in combination therewith, and permitting .the core to withdraw sufiicient heat from the'cast oxides to cause the casting to solidify adjacent the core and thereafter to cause the core to melt and flow out through said outlet.

4. In combination with a mold for use in easting refractory non-metallic material, a core formed of metal o high thermal conductivity and having a melting point below that of the material to be cast.

5. In combination with a mold for use in casting refractory material having a higher melting point than copper, a core of copper and a vent through which said copper can flow when molten,

6. In combination with a mold for use in cast ing fused aluminous materials, a core of copper.

'7. In combination with a mold for use in casting non-metallic refractory material, a core formed of metal of'high thermal conductivity and having a definite melting point below that of the material to be cast, and a vent through which said core material can flow when molten.

- CHARLES MQMUILEN. 

